This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-147997 filed on May 19, 2000.
1. Field of the Invention
The present invention relates to a vehicle communication device capable of communicating using a Dedicated Short-Range Communication (DSRC) radio system and to a device for checking the intensity of a radio wave emitted from the vehicle communication device through a windshield.
2. Related Art
The DSRC radio system is proposed in ARIB STD-T55 by Association of Radio Industries and Businesses (ARIB) as a standard for narrow area radio communication between a vehicle and a roadside device, and is currently used for an Electronic Toll Collection (ETC) system for a toll road. The DSRC radio system according to ARIB STD-T55 employs millimeter waves (5.8 GHz) for radio communication between a DSRC vehicle device (vehicle communication device) installed on a vehicle and a roadside radio device whose antenna is provided beside a road. Since the power of the millimeter waves is attenuated in a great ratio to distance, each communication area can be formed to be small (approximately 3-30 m). Furthermore, the communication areas are separated individually and therefore radio communication is implemented reliably, since the millimeter waves have a tendency not to leak outside the communication area and not to interfere in the communication area. Further, processing for communication can be performed fast and can be completed while the traveling vehicle stays in the small communication area, since the millimeter waves provide high-traffic communication (1.024 Mbps).
According to the DSRC radio system, the roadside radio device transmits a frame, and the DSRC vehicle device emits a radio wave as a response to the frame mainly based on the Frame Control Message Channel (FCMC). That is, the DSRC vehicle device in the communication area formed by the roadside radio device receives a pilot signal transmitted from the roadside radio device, and transmits a response signal to the roadside radio device. In this way, communication between the vehicle device and the roadside device is performed. Therefore the DSRC vehicle device outside the communication area is in a wait state and does not emit a radio wave.
The DSRC vehicle device is installed on, for example, the dashboard of the vehicle so that it can communicate with the roadside radio device through the windshield of the vehicle. However, if the windshield is made of heat reflecting glass, it includes conducting film inside and therefore has very low radio wave transmittance. When the DSRC vehicle device communicates through such a windshield, failure may occur or it cannot communicate at all. Accordingly, it is required to check radio wave transmittance of the windshield beforehand. Specifically, it is required to determine whether the windshield has sufficiently high radio wave transmittance for the DSRC vehicle device to communicate through the windshield.
The transmittance of the windshield may be checked by actually performing communication between the DSRC vehicle device and the roadside radio device through the windshield. However, it is bothersome to move the vehicle to a place where the ETC system is implemented for checking the transmittance of the windshield before the vehicle is delivered to a user. It is also not realistic to install a roadside radio device in a service or repair shop in which a DSRC vehicle device is installed in the vehicle, since the roadside radio device is relatively large and expensive.
The present invention has an object to provide a vehicle communication device which is installed in a vehicle and capable of continuously emitting a radio wave through the windshield of the vehicle so that the intensity of the radio wave may be checked by using a commercially available radio wave measuring instrument.
The present invention has another object to provide a device for checking the intensity of the radio wave emitted from the vehicle communication device through the windshield.
The vehicle communication device according to the present invention is installed in a vehicle and communicates with an external roadside radio device using a DSRC radio system. The vehicle communication device can be switched between a normal mode and an emitting mode. The vehicle communication device in the normal mode waits for a pilot signal from the roadside radio device, and transmits a response signal in response to receiving the pilot signal similarly to a conventional vehicle communication device. The vehicle communication device is switched to the emitting mode when a staff in a service or repair shop performs a specific operation. The vehicle communication device in the emitting mode continuously emits a radio wave through the windshield of the vehicle independently of whether it receives the pilot signal from the roadside radio device.
Preferably, the specific operation performed by the staff in a service or repair shop is designed so as to prevent accidental use by a user of the vehicle. For example, this specific operation may be a combination of an operation of control switches provided on the vehicle communication device and an operation of another vehicle device.
The checking device according to the present invention receives the radio wave emitted from the vehicle communication device in the emitting mode, and determines whether the intensity of the received radio wave is greater than a predetermined threshold. The result of the determination is reported to the staff in the service or repair shop. The staff can determine whether the vehicle communication device can be used for an ETC or other DSRC system based on the reported result. The vehicle communication device in the emitting mode is automatically switched to the normal mode when a predetermined time elapses after it is switched to the emitting mode.